From: Andy Shevchenko <andy.shevchenko@gmail.com>
To: Saravana Kannan <saravanak@google.com>
Cc: Grant Likely <grant.likely@arm.com>,
Linux Doc Mailing List <linux-doc@vger.kernel.org>,
LKML <linux-kernel@vger.kernel.org>, nd <nd@arm.com>,
Jonathan Corbet <corbet@lwn.net>,
Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Subject: Re: [PATCH] Add documentation on meaning of -EPROBE_DEFER
Date: Sat, 28 Mar 2020 13:13:42 +0200 [thread overview]
Message-ID: <CAHp75VdXG2vGNp-0DLqAMx377nwyjzEt5=+Nakg4_vhaDGZB-A@mail.gmail.com> (raw)
In-Reply-To: <CAGETcx_0=W6P_Zf-6fvDfncXUrPvt31bf6de-RWwHaXtwJizmQ@mail.gmail.com>
On Sat, Mar 28, 2020 at 1:57 AM Saravana Kannan <saravanak@google.com> wrote:
> On Fri, Mar 27, 2020 at 4:25 PM Grant Likely <grant.likely@arm.com> wrote:
> > On 27/03/2020 18:10, Saravana Kannan wrote:
> > > On Fri, Mar 27, 2020 at 10:01 AM Grant Likely <grant.likely@arm.com> wrote:
> > >>
> > >> Add a bit of documentation on what it means when a driver .probe() hook
> > >> returns the -EPROBE_DEFER error code, including the limitation that
> > >> -EPROBE_DEFER should be returned as early as possible, before the driver
> > >> starts to register child devices.
...
> > >> +Optionally, probe() may return -EPROBE_DEFER if the driver depends on
> > >> +resources that are not yet available (e.g., supplied by a driver that
> > >> +hasn't initialized yet). The driver core will put the device onto the
> > >> +deferred probe list and will try to call it again later. If a driver
> > >> +must defer, it should return -EPROBE_DEFER as early as possible to
> > >> +reduce the amount of time spent on setup work that will need to be
> > >> +unwound and reexecuted at a later time.
> > >> +
> > >> +.. warning::
> > >> + -EPROBE_DEFER must not be returned if probe() has already created
> > >> + child devices, even if those child devices are removed again
> > >> + in a cleanup path. If -EPROBE_DEFER is returned after a child
> > >> + device has been registered, it may result in an infinite loop of
> > >> + .probe() calls to the same driver.
> > >
> > > The infinite loop is a current implementation behavior. Not an
> > > intentional choice. So, maybe we can say the behavior is undefined
> > > instead?
Why? *Good* documentation must describe the actual behaviour, not hide it.
> > If you feel strongly about it, but I don't have any problem with
> > documenting it as the current implementation behaviour, and then
> > changing the text if that ever changes.
>
> Assuming Greg is okay with this doc update, I'm kinda leaning towards
> "undefined"
I think it should not distort the reality.
> because if documented as "infinite loop" people might be
> hesitant towards removing that behavior.
This is funny argument. Won't we do kernel better?
> But I'll let Greg make the
> final call. Not going to NACK for this point.
--
With Best Regards,
Andy Shevchenko
next prev parent reply other threads:[~2020-03-28 11:13 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-03-27 17:01 [PATCH] Add documentation on meaning of -EPROBE_DEFER Grant Likely
2020-03-27 18:10 ` Saravana Kannan
2020-03-27 23:25 ` Grant Likely
2020-03-27 23:55 ` Saravana Kannan
2020-03-28 11:13 ` Andy Shevchenko [this message]
2020-03-28 17:03 ` Jonathan Corbet
2020-03-28 21:46 ` Saravana Kannan
2020-03-31 14:33 ` Andy Shevchenko
2020-03-31 16:43 ` Greg Kroah-Hartman
2020-03-31 17:03 ` Andy Shevchenko
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